Microfluidic medical devices for processing blood may be used to introduce oxygen or clear undesirable particles from the blood of a patient. These microfluidic devices can include blood distribution manifolds coupled to processing channels. The processing channels of the device may not all lie within a single plane. Distribution of blood to the non-coplanar processing channels can be accomplished by a plenum. However, plenums typically require large priming volumes and do not permit the ability to control distribution of flow to individual conduits. Alternatively, a series of manifolds each having distribution channels in a one plane may be used, but a single planar manifold is incapable of distributing blood to non-coplanar processing channels.